Double wall combustor arrangement

ABSTRACT

A double wall structure for a combustor of a gas turbine engine comprising an inner wall, an outer wall and a rail assembly, the inner wall formed by discrete tiles, wherein each tile is secured to the outer wall by the rail assembly.

[0001] This invention relates to improvements to a combustor of a gasturbine engine and in particular to a heat resistant tile of a combustorwall.

[0002] In a double walled combustor of a gas turbine engine it is knownto provide an inner wall which comprises tiles with pedestals extendingtoward the outer wall thereby improving heat removal by the coolingfluid flow between the walls. The tiles are secured to the outer wall bybrazed studs, which are so arranged to allow the tiles to expand andcontract with the thermal cycle of the engine. However, the studs have atendency to “lock up” preventing the tile from undergoing thermalmovements. This problem is particularly significant at the downstreamedge of the tile, which distorts away from the outer wall. Where thisoccurs the cooling flow does not properly flow through the pedestalsthus reducing the cooling efficiency. This results in the trailing edgeundergoing some oxidation at elevated temperatures and there is then atendency for spalling of the trailing edge to occur.

[0003] U.S. Pat. No. 4,555,901 discloses a frictionally slideablemounted combustor liner assembly employing a tongue and groove typearrangement and a retaining ring. The circumferentially segmented linerpanels are assembled in axially rearward sequence. The liner andcombustor structural wall are independent of the structural and thermalstresses of each other. However, a disadvantage of the assembly is thatfailure of an upstream tile would intrinsically lead to the downstreamtile failing. A further disadvantage is that removal of an upstream tilemay only be facilitated by removal of downstream tiles first.

[0004] It is the object of the present invention to provide an improvedmounting assembly to allow tiles to expand and contract with the thermalcycles of the combustor and a stiffer tile.

[0005] According to the present invention a double wall structure for acombustor of a gas turbine engine comprises an inner wall, an outer walland a rail assembly, the inner wall formed by discrete tiles, whereineach tile is secured to the outer wall by the rail assembly.

[0006] It is an advantage of the present invention to provide combustortiles which, in use, are able to freely expand and contract during thethermal cycle of the gas turbine engine combustor. It is also anadvantage of the present invention that the tiles are securedindependently from one another, to the outer combustor wall, thusfailure of one tile does not lead to failure of another. It is also anadvantage of the present invention to provide a stiffer tile and inparticular a stiffer tile downstream edge.

[0007] A further advantage of the present invention is that individualor circumferential rows of tiles may be assembled or disassembledindependently without first placing or removing a downstream tile or rowof tiles.

[0008] Preferably, the gas turbine engine comprises a main engine axisand the combustor is annular and generally coaxial with the main engineaxis and the rail assembly is substantially annular and coaxial withrespect to the main engine axis.

[0009] Preferably, the rail assembly comprises co-operating andgenerally L-shaped cross-section hook features, the inner wall and outerwall define a gap therebetween and the hook features extend generallyinto the gap, one hook feature attached to the tile and one attached tothe outer wall so that, in use, the hook features co-operate to securethe tile to the outer wall.

[0010] Alternatively, the inner wall and outer wall define a gaptherebetween and the rail assembly comprises a generally T-shaped hookfeature and generally L-shaped hook features, the T-shaped hook featureattached to the tile and co-operating with the L-shaped hook featuresattached to the outer wall, the hook features extend into the gap andco-operate to secure the tile to the outer wall.

[0011] Preferably, wherein a generally L-shaped cross-section hookfeature defines a loading gap, the loading gap provided to allow thetiles to be assembled to the outer wall of the combustor.

[0012] Preferably, the rail assembly comprises a locking key, thelocking key so configured to, in operation, substantially fill theloading gap and thereby secure the tiles to the outer wall.

[0013] Preferably, the rail assembly comprises a locking plate.

[0014] Preferably, the tile comprises an edge and the rail assembly islocated in close proximity to the edge of the tile to provide stiffeningthereof.

[0015] Preferably the tile comprises an edge and the edge of the tile isprofiled and the profiled edge of the tile comprises an end wall.

[0016] Alternatively, the profiled edge of the tile comprises a coolingpassage.

[0017] Embodiments of the invention will now be described by way ofexample only, with reference to the accompanying diagrammatic drawings,in which:

[0018]FIG. 1 is a sectional side view of a gas turbine engine.

[0019]FIG. 2 shows a prior art sectional side view of part of acombustor of the engine shown in FIG. 1;

[0020]FIG. 3 shows a prior art sectional side view of a part of aradially outer wall structure of a combustor showing a wall element;

[0021]FIG. 4 is a sectional side view of part of a radially inner wallstructure of a combustor showing a wall element of the presentinvention;

[0022]FIG. 5 is a sectional side view of a radially inner wall of acombustor showing a wall element of an embodiment of the presentinvention.

[0023]FIG. 6 is an isometric cut away view of tiles mounted on aradially outer wall of a combustor showing assembly details of thepresent invention.

[0024]FIG. 6A is a sectioned view of a locking plate.

[0025]FIG. 6B is an isometric view of a locking key.

[0026]FIG. 7 is a sectional side view of tiles mounted on a radiallyouter wall of a combustor showing a wall element of an embodiment of thepresent invention.

[0027]FIG. 8 is a sectional side view of tiles mounted on a radiallyouter wall of a combustor showing a wall element of an embodiment of thepresent invention.

[0028] With reference to FIG. 1, a ducted fan gas turbine enginegenerally indicated at 10 has a principal axis X-X. The engine 10comprises, in axial flow series, an air intake 11, a propulsive fan 12,an intermediate pressure compressor 13, a high pressure compressor 14,combustion equipment 15, a high pressure turbine 16, an intermediatepressure turbine 17, a low pressure turbine 18 and an exhaust nozzle 19.

[0029] The gas turbine engine 10 works in the conventional manner sothat air entering the intake 11 is accelerated by the fan to produce twoair flows: a first air flow into the intermediate pressure compressor 13and a second air flow which provides propulsive thrust. The intermediatepressure compressor 13 compresses the air flow directed into it beforedelivering that air to the high pressure compressor 14 where furthercompression takes place.

[0030] The compressed air exhausted from the high pressure compressor 14is directed into the combustion equipment 15 where it is mixed with fueland the mixture combusted. The resultant hot combustion products thenexpand through, and thereby drive, the high, intermediate and lowpressure turbine 16, 17 and 18 before being exhausted through the nozzle19 to provide additional propulsive thrust. The high, intermediate andlow pressure turbines 16, 17 and 18 respectively drive the high andintermediate pressure compressors 14 and 13 and the fan 12 by suitableinterconnecting shafts.

[0031] Referring to FIG. 2, the prior art combustor 15 is constituted byan annular combustion chamber 20 having radially inner and outer wallstructures 21 and 22 respectively. The combustor 15 is secured to a wall23 by a plurality of pins 24 (only one of which is shown). Fuel isdirected into the chamber 20 through a number of fuel nozzles 25 locatedat an upstream end 26 of the chamber 20. The fuel nozzles 25 arecircumferentially spaced around the engine 10 and serve to spray fuelinto air derived from the high pressure compressor 14. The resultantfuel/air mixture is then combusted within the chamber 20.

[0032] The combustion process which takes place within the chamber 20naturally generates a large amount of heat. It is necessary, therefore,to arrange that the inner and outer wall structures 21 and 22 arecapable of withstanding the heat.

[0033] The radially inner and outer wall structures 21 and 22 eachcomprise an outer wall 27 and an inner wall 28. The inner wall 28 ismade up of a plurality of discrete wall elements in the form of tiles29A and 29B.

[0034] Each of the tiles 29A, 29B has circumferentially extending edges30 and 31, and the tiles are positioned adjacent each other, such thatthe edges 30 and 31 of adjacent tiles 29A, 29B overlap each other.Alternatively, the edges 30, 31 of adjacent tiles can abut each other.Each tile 29A, 29B comprises a base portion 32 which is spaced from theouter wall 27 to define therebetween a space 44 (see FIG. 3) for theflow of cooling fluid in the form of cooling air as will be explainedbelow. Heat removal features in the form of pedestals 45 (see FIG. 3)are provided on the base portion 32 and extend into the space 44 towardsthe outer wall 27.

[0035] Conventionally, and as shown in the prior art arrangement of FIG.2, securing means are in the form of studs 35 comprising threaded plugs34 and nuts 36. Each tile 28 has a plurality of threaded plugs 34extending from the base portions 32 of the tiles 29A, 29B throughapertures in the outer wall 27. Nuts 36 are screwed onto the plugs 34 tosecure the tiles 29A, 29B to the outer wall 27.

[0036] Referring to FIG. 3, during engine operation, some of the airexhausted from the high pressure compressor 14 is permitted to flow overthe exterior surfaces of the chamber 20. The air provides chamber 20with cooling and some of the air is directed into the interior of thechamber 20 to assist in the combustion process. First and second rows ofmixing ports 38, 39 are provided in the tiles 29B and are axially spacedfrom each other. The ports 38 correspond to apertures 40 in the outerwall 27, and the ports 39 correspond to apertures 41 in the outer wall27.

[0037] Referring particularly to the tiles 29B, arrow A in FIG. 3indicates air exiting via the open upstream edge 30 of the tile 29B andmixing with downstream air flowing from the upstream adjacent tile 29A,as indicated by arrow B The arrow C indicates the resultant flow of air.Angled effusion holes 46 are provided centrally of the tile 293 betweenthe ports 38 and 39. Arrow D indicates a flow of air exiting from thespace 44 through the holes 46. Also, a flow of downstream air exits fromthe open downstream edge 31 of the tile 29B after mixing with upstreamair flowing from the adjacent tile 29A, as indicated by arrow E. Airflows indicated by arrows C and E provide a film of cooling air over theinterior surface of the tiles 29A and 29B thereby preventing overheatingcaused by the combustion of gases in the chamber 20.

[0038] During a normal operation cycle of the engine 10 the combustor 20will be subject to varying amounts of combustion heat. This causes thetiles 29A and 29B to thermally expand relative to the outer wall 27.These thermal expansions are usually accommodated by the studs 35 whichallow the tiles 29A and 29B to slide. During the working life of thiscombustor wall arrangement, although relatively rare, the studs 35 havea tendency to lock-up and prevent the tiles from thermally expanding.This problem is particularly significant at the downstream edge 31 ofthe tiles 29A and 29B, which then distorts away from the outer wall 27.Where this occurs, the cooling flow, through the space 44, does notproperly flow through and around the pedestals which in turn reduce thecooling efficiency and effectiveness of the tiles. This results in thetrailing edge 31 undergoing oxidation at elevated temperatures and thereis then a tendency for spalling of the trailing edge 31 to occur. Thismay ultimately lead to a complete failure of the combustor wall 20 andmay lead to the combustor flame breaking though the wall 20.

[0039]FIG. 4 is a sectional side view of part of a wall structure of acombustor showing a wall element of the present invention and is apreferred embodiment. The studs 35 of the prior art have been replacedwith rail assemblies 48, 54 to secure the tiles 29A, 29B to the outerwall 27. The rail assemblies 48, 54 comprise co-operating hook features50, 52 and 56, 58 respectively. Hooks 50 and 56 are attached to tile29A, and hooks 52 and 58 are attached to outer wall 27. Each hookfeature 50, 52 and 56, 58 is cast integrally with the tiles 29A, 29B andouter wall 27 or alternatively the hooks feature 50, 52 and 56, 58 maybe attached by brazing or welding.

[0040] Each hook 50, 52, 56, 58 is of substantially L-shapedcross-section and comprises a flange 60, substantially oriented in thedirection Y-Y, and a web 62 extending substantially perpendicular to theY-Y axis from the tile 29A, 29B or outer wall 27, the flange 60 beingdisposed to the distal end of the web 62 from the tiles 29A, 29B orouter wall 27 accordingly. The web 62 defines a plurality of holes 66through which cooling air passes.

[0041] As shown in FIG. 4, the rail assemblies 48, 54 are oriented so asto operate in co-operative association with one another, hook 50opposing relative upstream displacement and hook 56 opposing relativedownstream displacement of the tile 29A, 29B. Alternatively, theorientation of the hooks 48, 54 may be reversed.

[0042] It is an advantage to use rail assemblies 48, 54, as shown inFIG. 4, as thermal expansions in the Y-Y axis direction may be easilyaccommodated by a gap 64 between the distal end of the flange 60 and theweb 62 of the cooperating hook. Thermal expansions and contractions inthe plane of the tile 29A, 29B and perpendicular to the axis YY may alsobe accommodated by the rail arrangement 48, 54 as sliding may take placefreely in that direction.

[0043] It is a further advantage of the rail arrangement 48, 54 that theweb 62 and flange 60 arrangement contributes to an increase in thestiffness of the tile 29A, 29B. To this effect the rail arrangement 54is positioned near to the edge 30 of the tile 29A, 29B, thereby furtherreducing the Likelihood of the edge 30 distorting out of its originalplane as a consequence of thermal expansion.

[0044] Furthermore, FIG. 4 illustrates profiling of the tile edge 30 inorder to further increase the stiffness locally of the tile 29A, 29Bedge 30. The profiling may take many forms, of which two are shown inFIGS. 7 and 8 and are discussed in more detail below.

[0045] Referring now to FIG. 5, which shows a second rail arrangement69. The second rail arrangement 69 is configured in a general andinverted T-shape with the flange 68 extending either side of the web 70.The flange 68 and web 70 are in operative association with hooks 72 and74. Each tile 29A, 29B comprises at least one second rail arrangement69. The number of second rail assemblies 69 is dictated by the size ofeach tiles 29A, 29B, the thermal and structural stresses imposed on thetiles 29A, 29B and stiffness requirements thereof.

[0046] The T-shaped second rail arrangement 69 provides stiffening tothe tiles 29A, 29B in the same way as the substantially L-shapedcross-section hooks described hereinbefore and with reference to FIG. 4.Similarly, a gap 76 is designed to accommodate thermal expansionsthereby preventing deformation of the edges 30, 31 of the tiles 29A,29B.

[0047] Although FIG. 5 shows the generally T-shaped second rail assembly69 disposed to the tile 29A, it may equally effectively be disposed tothe outer wall 27 and the cooperating L-shaped cross-section hookfeatures 72, 74 may be disposed to the tile 29A.

[0048] Anti-frettage coating, as known in the art, may be provided toany contacting surfaces of the rail assemblies 48, 54 and second railassembly 69. The anti-frettage coatings also may be used to modify, andbeneficially so, the co-efficient of friction between contactingsurfaces.

[0049]FIG. 6 is an isometric cut away view of tiles 29A, 29B mounted onthe combustor wall 27 and shows details of the assembly of the tiles29A, 29B. The tiles 29A are assembled to the combustor wall 27 through aloading gap 78 in the substantially circumferential rails 48, 54 mountedon the outer wall 27. The tiles 29A are circumferentially disposedaround the combustor outer wall 27 and are abutted to one another.

[0050] There is a tendency for the tiles 29A to displacecircumferentially during normal engine 10 operation and a locking plate80 is used to prevent this circumferential movement.

[0051]FIG. 6A shows the locking plate 80 in more detail. The lockingplate 80 is attached to the combustor outer wall 27 by conventionalmeans and in this case is attached by a threaded extension 88 whichco-operates with a washer 84 and nut 86. The plate 82 blocks thecircumferential path of the co-operating hook feature 52 of the tile29A. Further locking plates 80 may be located around the rail assemblies48, 54 at suitable locations.

[0052]FIG. 6B shows a locking key 90 which is used to retain the tiles29A where there is a discontinuity in the hook feature 50 of thecombustor outer wall 27. The locking key 90 is secured to the outer wall27 by conventional securing means including the means as described abovefor the locking plate 80. It is preferable to arrange the tiles 29A suchthat approximately half their circumferential length extends into theloading gap 78. The loading gap 78 may then be partially or entirelyfilled by the locking key 90. The locking key 90 may comprise more thanone securing means.

[0053] A further advantage of the present invention is that where tworail assemblies 48, 54 are utilised to secure a Circumferential row oftiles 29A only one of the rail assemblies 48 is required to have aloading gap 78. Thus the co-operating hook feature 56 of the railassembly 54 (FIG. 4) may be completely annular and therefore carry hoopstresses, present in the combustor outer wall 27 of both or one of theradially inner wall 21 and radially outer wall 22, derived from the highpressure air egressing from the high pressure compressor 14 andcombustion heat.

[0054] This enables the outer wall 27 to be constructed of thinnermaterial or permitted to carry a greater load.

[0055] It should be noted that the term rail assembly 48, 54 comprisesthe co-operating L-shaped hook features 50, 52, and 56, 58 and may alsocomprise the loading gap 78, the locking key 90 and the locking plate80.

[0056] Referring to FIG. 7 which is a sectional side view of tile 29Amounted on a radially outer wall 27 of a combustor 15 showing a wallelement of an embodiment of the present invention. The tile edge 30comprises a profiled configuration having a cooling passage 92therethrough.

[0057] The cooling passage 92 increases the cooling and stiffness of theedge 30 of the tiles 29A thereby rendering the edge 30 less susceptibleto thermal distortions.

[0058]FIG. 8 is a sectional side view of tiles 29A mounted on a radiallyouter wall 27 of a combustor 15 showing a wall element of an embodimentof the present invention.

[0059] This embodiment comprises a thickened end wall 94 which providesincreased stiffness to the edge 30 of the tile 29A.

[0060] The various embodiments of the geometric configuration of theprofiled tile edge 30 may easily be made to increase the stiffnessthereof, but are intended to be within the scope of the presentinvention.

[0061] A further advantage of the present invention and one that ispartially shown in FIG. 3 is that the tiles 29A, 29B are independentlysecured to the outer wall 27. This has the advantage that failure of onetile 29A, 29B does not lead to failure of another adjacent tile.

[0062] The rail assembly 48, 54, 69 also permits individualcircumferential rows of tiles 29A, 29B to be fitted and disassembled tothe combustor outer wall 27 without disturbing upstream or downstreamcircumferential rows of tiles 29A, 29B. The configuration of the railassembly 48, 54, 69 and the circumferential rows of tiles 29A, 29B meansthat failure of one tile 29A, 29B does not lead to failure ordisturbance of an upstream or downstream tile 29A, 29B.

[0063] Whilst endeavouring in the foregoing specification to drawattention to those features of the invention believed to be ofparticular importance it should be understood that the Applicant claimsprotection in respect of any patentable feature or combination offeatures hereinbefore referred to and/or shown in the drawings whetheror not particular emphasis has been placed thereon.

I claim:
 1. A double wall structure for a combustor of a gas turbineengine comprising an inner wall, an outer wall and a rail assembly, theinner wall formed by discrete tiles, wherein each tile is secured to theouter wall by the rail assembly.
 2. A double wall structure for acombustor of a gas turbine engine as claimed in claim 1 wherein the gasturbine engine comprises a main engine axis and the combustor is annularand generally coaxial with the main engine axis and the rail assembly issubstantially annular and coaxial with respect to the main engine axis.3. A double wall structure for a combustor of a gas turbine engine asclaimed in claim 1 wherein the rail assembly comprises co-operating andgenerally L-shaped cross-section hook features, the inner wall and outerwall define a gap therebetween and the hook features extend generallyinto the gap, one hook feature attached to the tile and one attached tothe outer wall so that, in use, the hook features co-operate to securethe tile to the outer wall.
 4. A double wall structure for a combustorof a gas turbine engine as claimed in claim 1 wherein the inner wall andouter wall define a gap therebetween and the rail assembly comprises agenerally T-shaped hook feature and generally L-shaped hook features,the T-shaped hook feature attached to the tile and co-operating with theL-shaped hook features attached to the outer wall, the hook featuresextend into the gap and co-operate to secure the tile to the outer wall.5. A double wall structure for a combustor of a gas turbine engine asclaimed in claim 3 wherein the generally L-shaped cross-section hookfeature defines a loading gap, the loading gap provided to allow thetiles to be assembled to the outer wall of the combustor.
 6. A doublewall structure for a combustor of a gas turbine engine as claimed inclaim 5 wherein the rail assembly comprises a locking key, the lockingkey so configured to, in operation, substantially fill the loading gapand thereby secure the tiles to the outer wall.
 7. A double wallstructure for a combustor of a gas turbine engine as claimed in claim 1wherein the rail assembly comprises a locking plate.
 8. A double wallstructure for a combustor of a gas turbine engine as claimed in claim 1wherein the tile comprises an edge and the rail assembly is located inclose proximity to the edge of the tile to provide stiffening thereof.9. A double wall structure for a combustor of a gas turbine engine asclaimed in claim 1 wherein the tile comprises an edge and the edge ofthe tile is profiled.
 10. A double wall structure for a combustor of agas turbine engine as claimed in claim 9 wherein the profiled edge ofthe tile comprises an end wall.
 11. A double wall structure for acombustor of a gas turbine engine as claimed in claim 9 wherein theprofiled edge of the tile comprises a cooling passage.